Fair Value of Financial Instruments (Details-3)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Basis adjustment:
Basis adjustment - on peak	98.10%	94.20%
Basis adjustment - off peak	95.00%	92.60%
US Treasury Bills [Member]
Deferred compensation plan
Investment interest calculation, investment maturity period (26 weeks)	182 days
Investment interest calculation, monthly compounding rate	1.00%
Investment interest calculation, minimum annual rate compounded monthly	7.00%
Minimum [Member]
Counterparty fuel mix:
Internal generation	50.00%	50.00%
Purchased power	30.00%	30.00%
Maximum [Member]
Counterparty fuel mix:
Internal generation	70.00%	70.00%
Purchased power	50.00%	50.00%

Investment maturity period used in deferred compensation interest calculation.

No definition available.

Name:	mgee_DeferredCompensationArrangementWithIndividualInvestmentInterestCalculationInvestmentMaturityPeriod
Namespace Prefix:	mgee_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum annual rate compounded monthly used in deferred compensation interest calculation.

+ References

No definition available.

+ Details

Name:	mgee_DeferredCompensationArrangementWithIndividualInvestmentInterestCalculationMinimumAnnualRateCompoundedMonthly
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage increase compounded monthly used in deferred compensation interest calculation.

+ References

No definition available.

+ Details

Name:	mgee_DeferredCompensationArrangementWithIndividualInvestmentInterestCalculationMonthlyCompoundingRate
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	mgee_FairValueInputsBasisAdjustmentAbstract
Namespace Prefix:	mgee_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	mgee_FairValueInputsCounterpartyFuelMixAbstract
Namespace Prefix:	mgee_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Estimate of counterparty's internal generation as a portion of their fuel mix, used as an input to measure fair value.

+ References

No definition available.

+ Details

Name:	mgee_FairValueInputsCounterpartyFuelMixInternalGeneration
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Estimate of counterparty's purchased power as a portion of their fuel mix, used as an input to measure fair value.

+ References

No definition available.

+ Details

Name:	mgee_FairValueInputsCounterpartyFuelMixPurchasedPower
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Basis adjustment between delivery points for off peak electric future prices. Used as an input to measure fair value.

+ References

No definition available.

+ Details

Name:	mgee_FairValueInputsDeliveryPointsBasisAdjustmentOffPeak
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Basis adjustment between delivery points for on peak electric future prices. Used as an input to measure fair value.

+ References

No definition available.

+ Details

Name:	mgee_FairValueInputsDeliveryPointsBasisAdjustmentOnPeak
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DeferredCompensationArrangementsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USTreasuryBillSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: